Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Photoisomerization is molecular behavior in which a structural change between isomers is caused by photoexcitation. Photoisomerization can be observed in compounds having trans and cis isomers such as azobenzene, stilbene and their derivatives. This class of compounds may have a double bond, and rotation or inversion around the double bond may allow isomerization between the trans and cis states upon irradiation with particular wavelengths of light.
For instance, azobenzene is a chemical compound composed of two phenyl rings linked by an N═N double bond. The term “azobenzene” or simply “azo” may be used to refer to a class of molecules that share a core azobenzene structure, with different chemical functional groups extending from the phenyl rings. Azobenzene has two types of isomers, trans and cis isomers. One of the interesting properties of azobenzene (and its derivatives) is photoisomerization between the trans and cis isomers. The trans-azobenzene isomer is more stable than the cis-azobenzene isomer by approximately 50 kJ/mol (about 12 kcal/mol), and a barrier to the trans-cis photoisomerization is approximately 200 kJ/mol (about 48 kcal/mol). Therefore, azobenzene can absorb heat energy from an atmosphere or release heat energy into an atmosphere through the trans-cis photoisomerization.